Ink compositions containing charged particles are used in a wide variety of applications such as electro-conductive additives to plastics, toners in electrophotography printing, pigmented ink, electrophoretic display as well as many other applications. Such inks are often referred to as electronic inks. Such electronic inks traditionally include charged particles, such as colorant particles, in order to help the particles to respond to electric field.
Currently, charged particles that are used in electronic ink materials or in electrophoretic display materials, as examples, are mostly negatively charged. This unidirectional charging mechanism often limits the design of devices. Indeed, as an example, when particles are pigments, the negative charge limits device architecture to have stacked layers in order to accommodate multiple colors. As an example, such architecture often results in that most of the light incident to the display is scattered by the top layers and, therefore, insufficient light reaches the bottom layer which lead thus to performance issues such as low optical density.
Many methods have been proposed to produce such positively charged inks. However, investigations continue into developing positively charged inks.